The present invention relates to a driving apparatus with a commutator-less motor which may be used in driving cylinder drum motors of video tape recorders, spindle motors of floppy disc drive units and the like.
Commutator-less motors have recently been used widely in video tape recorder and floppy disk driving apparatus.
In a motor for driving the cylinder drum of a video tape recorder, in order to detect the rotating position of the rotary magnetic head of the drum, it is necessary to generate a pulse signal called a phase generator signal (PG signal) once each time the rotor of the motor coupled to the drum makes one revolution. On the other hand, in the spindle motor of a floppy disc driving apparatus, in order to detect the write starting position of the floppy disc, it is also necessary to generate a pulse signal called an index signal once each time the motor rotor makes one revolution.
FIG. 17 shows the construction of a conventional commutator-less motor for obtaining such pulse signals.
In FIG. 17, a stator substrate 2 is mounted on the surface of a stator yoke 1, and a stator winding 3 and a rotating position detecting element 4 are disposed on the surface of the stator substrate 2. In the center of the stator yoke 1 and stator substrate 2, a bearing housing 5 is affixed. In the center of the bearing housing 5, a shaft 7 is rotatably installed through a ball bearing mechanism 6. At the upper end portion of the shaft 7, the center of rotor yoke 8 is affixed. On the lower surface of the rotor yoke 8, a rotor magnet 9 is fitted. At one position on the outer circumference of the rotor yoke 8, a PG (phase generator) magnet 10 is installed in order to generate one pulse signal every time the rotor yoke 8 makes a revolution. Above the stator substrate 2, a hall IC 11 is positioned opposite to the rotation track of the PG magnet 10.
FIG. 18 shows a conventional three-phase motor driving circuit for driving the commutator-less motor in FIG. 17.
In FIG. 18, three rotating position detecting elements (CH.sub.1, H.sub.2, H.sub.3) connected parallel between a power source 12 and ground. The output terminals of the rotating position detecting elements (H.sub.1, H.sub.2, H.sub.3) are respectively connected to input terminals of amplifiers 13, 14, 15. The output terminals of the amplifiers 13, 14, -5 are connected to input terminals of three subtraction circuits 16, 17, 18 which are connected as shown in FIG. 18. Output signals of the subtraction circuits 16, 17, 18 are processed in current driving circuits, 19, 20, 21, and then amplified. Output currents I.sub.p1, I.sub.p2, I.sub.p3 of the current driving circuits 19, 20, 21 are supplied to stator windings 3 (L.sub.1, L.sub.2, L.sub.3), disposed on the surface of the stator substrate 2, as driving currents.
The three-phase motor driving circuit shown in FIG. 18 supplies the driving currents I.sub.p1, I.sub.p2, I.sub.p3 to three stator windings 3 (L.sub.1, L.sub.2, L.sub.3) according to the output signals of three rotating position detecting elements 4 (H.sub.1, H.sub.2, H.sub.3), and rotates the rotor yoke 8 by making use of the electromagnetic action between the stator windings 3 (L.sub.1, L.sub.2, L.sub.3) and the rotor magnet 9, This operation itself has been known well, and is not specifically described herein.
When the rotor yoke 8 of the motor in FIG. 18 is put into revolution by the three-phase motor driving circuit of FIG. 18, the PG magnet 10 passes near the Hall IC 11 every time the rotor yoke 8 makes one revolution. As a result, the Hall IC 11 detects the magnetic flux of the PG magnet 10, and generates a PG signal. Accordingly, this PG signal is used in, for example, detection of rotating position of the rotary magnetic head in a video tape recorder, or detection of write starting position of floppy disc in floppy disk driving device.
However, in the construction shown in FIGS. 17, 18, the PG magnet 10 must be glued to the outer circumference of the rotor yoke 8 with adhesive or the like, and also the Hall IC 11 must be attached to the stator substrate 2. Accordingly, this increases the number of parts and the number of assembling steps required, and impairs productivity. Still more, when an ordinary ferrite magnet is used as the PG magnet 10, a sufficient sensitivity is not obtained, and hence an expensive rare earth magnet or the like must be used as the PG magnet 10. Accordingly, the material cost is also increased. This is in addition to the elevation of cost due to the increased number of parts and number of assembling steps required in conventional construction.
The present invention is intended to present a commutator-less motor driving apparatus, capable of solving such conventional problems.
It is hence a first object of the invention to provide a commutator-less motor driving apparatus capable of generating one pulse signal in every revolution of the motor by electrical signal processing, without using any special parts such as a PG magnet or a Hall IC.
It is a second object of the invention to provide a commutator-less motor driving apparatus capable of reducing the fluctuations of driving torque of the motor caused by the addition of such mechanical devices for generating pulse signals.
It is a third object of the invention to provide a commutator-less motor driving apparatus capable of enhancing the detection precision of such pulse signals.
It is a fourth object of the invention to provide a driving apparatus of a commutator-less motor capable of electrically fine-adjusting the error due to mechanical deviation at the time of assembling of the motor by electrically delaying such pulse signals.
It is a fifth object of the invention to provide a delay circuit preferably used for delaying pulse signals.
The present inventors previously filed an application, dated Feb. 6, 1990, (Ser. No. 07/475,771) for a similar invention of which this invention is an improvement.